Evaluation of spatially fractionated(GRID)radiotherapy using a multi-leaf collimator with the Vero4D

• 作 者: HajimeMonzen[1]ShinichiNakayama[2]MikotoTamura[1]YutakoOoyama[2]YuuichiOonishi[2]HirofumiEnomoto[2]KoheiShimomura[3]KenjiMatsumoto[3]MasahikoOkumura[3]SouichirouKaneshige[2]
• 机 构: Graduate School of Medicine,Kinki University,Department of Radiation Oncology,377-2 Ohno-higashi,Osa
• 出 处: The 15th Asia-Oceania Congress of Medical Physics (AOCMP2015
• 发表日期: 2015年期

　　Purpose:The efficacy of spatially fractionated(GRID)radiotherapy for treating bulky tumors has been recognized and demonstrated.GRID therapy might improve tumor control while reducing normal tissue toxicity.In this study,we evaluated the dosimetric characteristics of delivering GRID therapy using a multi-leaf collimator(MLC)with the Vero4DRT.Method:Four grid patterns were prepared with an(a)isolated or(b)adjacent pattern,and grid opening measuring 10×10 mm2 or 5×5 mm2 on the plane 100 cm from the source.These were referred to as GRID10a,GRID10b,GRID5a,and GRID5b.We used 6 MV xrays and irradiated EBT3 film to measure the valley-to-peak dose ratio(V-P ratio)which was defined as dose ratio in the blocked and opened areas at three depths(1.5,5,and 10 cm),with an actual irradiation size at 1.5 cm depth,using a water-equivalent phantom.Result:The respective V-P ratios with GRID10a,GRID10b,GRID5a,and GRID5b were about 6,13.5,15.4,and 35.6%at a depth of 1.5 cm,8.4,18.1,18.7,and 39.5%at 5 cm,and 10.8,22.7,21.7,and 44%at 10 cm.The actual irradiation sizes with the four patterns were 1.0,1.0,0.6,and 0.7 cm at inline and 1.2,1.2,0.6 and 0.7 cm at crossline,respectively.Conclusion:The Vero4DRT has features of low MLC transmission and shape penumbra and may enable the delivery of ablative doses for MLC-based GRID therapy.